Process for electrolytic oxidation of thallium or cerium salts



Dec. 30, 1969' TA. H. FRYE 3,486,992 v PROCESS FOR ELECTROLYTIC OXIDATION OF THALLIUM OR CERIUM SALTS Filed Feb. 15, 1967 4 Sheets-Sheet 1 I00 A CURVE B. 5 o

2 2 j 60 =1 E F 4o CURVEA Z 8 Y 5 2o- 0 1 l "I l l 0 20 4Q 50 so IOO DURATION OF ELECTROLYSIS (MIN),

FIG

SOLUTION o BE OXIDIZED QMEMBRANE /ANODE CATHODE- m LOXIDIZED SOLUTION GRAVITY FLOW CELL FIGZ INVENTOR ALFRED H. FRYE ATTORNEYS Dem3 0,*1969 A. H. FRYE 3,486,992

PROCESS FOR ELECTROLYTIC OXIDATION OF THALLIUM 0R CERIUMLSAL'IS Filed Feb. 15, 1967 4 Sheets-Sheet 2 v MEMBRANE v 4 FORCED FLOW CELL FIG.3

1 v -v v w D V 4 I- 4' a 4 h l h I I v "I' I SOLUTION OXIDIZED L L INVENTOR I v ALFRED H.FF\YE OXlDlZED I SOLUTION I M; A'rf r ws Dec. 30, 1969 A. H. FR'YE PROCESS FOR ELECTROLYTIC OXIDATION OF THALLIUM OR CERIUM'SALTS Filed Feb. 15, 1967 4 Sheets-Sheet S 0x11312513 'sol uT|0N MEMBRANE ,Q

CATHODE i PUMP PUMP s ugow INVENTOR Fig-4 ALFRED H.FRYE

OXIDIZED W W; ATTORNEYS Dec; 30, 1969 I A, H, F 3,486,992

PROCESS FOR ELECTROLYTIC OXIDATION OF THALLIUM OR CE-RIUMHSALTS Filed Feb. 15. 1 4 Sheets-Sheet 4 FIG-5 ME ANE YMBYR ANODE SURGE ,90 (\lQ- 2% o g 2 3X 0 10 U9 0 1!- (11$ 93' x0 0... 2 Om EB INVENTOR ALFRED H. FRYE ATTORNEYS United States Patent 3486.992 PROCESS FOR ELECTROLYTIC OXIDATION OF THALLIUM 0R CERIUM SALTS Alfred H. Frye. Loveland, Ohio, assignor to The Cincinnati Milling Machine Co., Cincinnati, Ohio, a corporation of Ohio Filed Feb. 15, 1967, Ser. No. 616,377 Int. Cl. B01k 1/00, 3/10; C07b 3/00 U.S. Cl. 204-86 4 Claims ABSTRACT OF THE DISCLOSURE DRAWINGS FIGURE I is a chart graphically showing the course of both oxidation and reduction of thallium sulfate solutions when subjected to electrolysis in an undivided cell. FIGURES II, III and IV are diagrammatic representation of several prototypic cells. All of the drawings will be described in detail in connection with a more detailed description of the invention.

Proposals have been made to use solutions of either thallium (III) or cerium (IV) salts as oxidizing agents for organic compounds, as for example, the use of thallium (III) acetate [U.S. 2,927,131], thallium (III) sulfate [U.S. 3,048,636], or cerium (IV) sulfate [R. Ramaswamy et al., Bull. Chem. Soc. Japan, 35, 1,751 (1962); W. S. Trahanovsky and L. E. Young, J. Chem. Soc., 1965, 5,777; I. Am. Chem. Soc., 31, 2033 [1966], but up to the present invention no method has been described which provides an efiicient and economically feasible way to reoxidize with high percent conversion the concomitantly formed lower valent ions, viz., thallium(I) or cerium (III), back to their higher valent states so that they may again be used in the oxidation of additional organic material.

The problems and deficiencies of the prior art, as well as the advantages of the present invention, may be more easily understood by reference to FIGURE I and the data summarized therein, which data were obtained in the following manner.

A cathode of platinized platinum foil having a surface area of 4 in. and an anode of bright platinum foil with a surface area of 8 in. were immersed in 200 ml. of a mechanically stirred aqueous solution of thallium(I) sulfate containing 0.07 g. ion of [Tl]+ and 0.24 g. ion [80 1- and electrolysis commenced using a current of 2.5 amps. The electrolysis was interrupted periodically and samples of the aqueous solution were withdrawn and analyzed for their thallium(I) content. From FIGURE I it is evident that the percent conversion levels off in the neighborhood of 55-60% thallium(III) and thereafter remains constant. (Incidentally, the current etficiency for the electrolysis drops from an initial value of 75% to a final value of 12%, the overall efficiency being 34%.) Accordingly, it may be assumed that in addition to the following electrode reactions- Cathode 3,486,992 Patented Dec. 30, 1969 the reduction of the electrolytically generated thallium (III) ion also occurs at the cathode, i.e.,

[Tl] +2e [Tl]+.

This assumption is confirmed by a complementary demonstration in which 200 ml. of an aqueous thallium (III) sulfate solution containing 0.07 g. ion [Tl]+ and 0.24 g. ion [80,] is electrolyzed under these same conditions. The resultant data are summarized in Curve B of FIGURE I. Obviously, if high conversions of thallium(I) to thallium(III) are to be achieved rapidly and with economically attractive current efficiencies, the unwanted reduction of the thallium(III) ion occurring at the cathode must be prevented or substantially diminished.

It is one of the objects of this invention to overc0me this problem and the deficiency in the prior art and to provide a novel and economically attractive process for reoxidizing thallium(I) and cerium(III) from their lower valent to their higher valent states.

A more specific object of this invention is to provide a method for the electrolytic reoxidation of solutions of salt of thallium(I) or of cerium(III) in such a way as not to introduce into those solutions any unwanted or deleterious materials, nor to alter the concentrations of the ions in such a way that their desired concentrations cannot easily and cheaply be reestablished.

Other objects and advantages of this invention Will appear hereinafter.

It has been found, according to this invention, that these objects can be achieved and high conversions of polyvalent metallic ion of lower valent state to higher valent state can be obtained by passing the solution to be oxidized first into the cathode compartment and then into the anode compartment of a divided electrolytic cell in which the anode compartment is separated from the cathode compartment by a water-permeable membrane or diaphragm which:

(1) Serves to impede the migration of the higher valent ion, the oxidized ion, from the anode compartment to the cathode compartment and yet, by being water-permeable, permits the all-essential transport of the current-carrying hydrogen ion through the membrane in that same direction. and

(2) Prevents the mixing of the gaseous hydrogen liberated at the cathode with the oxygen liberated at the anode, such mixtures being hazardously explosive.

In the practice of this invention it has been found that suitable membranes may be selected from such materials as reinforced cation or anion exchange resins, as for example those described inv U.S. 2,962,454, and U.S. 2,800,445, microfibreglass matting of the type supplied by the Gelman Instrument Company for thin layer chromatography, and the hydrophilically modified microporous membranes of poly(propylene) or of poly(tetrafluoroethylene), such as supplied by Bel-Arts Products, Inc. and by Chemplast, Inc.

In general, the electrode materials should, under the conditions in which they are to be used, have high resistance to chemical attack, and, in the case of the cathode, afford a sufficiently low hydrogen overvoltage to cause the liberation of hydrogen in preference to the reduction of the metal ion to its zero-valent state, whereas in the case of the anode, afford sufficiently high oxygen overvoltage to permit substantial oxidation of the metallic ion in competition with the liberation of oxygen and/or, via the intermediate agency of some adequately strong chemical oxidizing agent, e.g., lead dioxide or activated chemisorbed oxygen, being concomitantly generated at the anode-solution interface under the conditions of electrolysis. Thus, suitable cathode materials are such materials as platinized platinum and platinized titanium, and for the anode, materials such as bright or platinized platinum, platinized titanium, and lead.

In order that this invention may be more readily understood, it is illustrated and described by reference to the following drawings in which FIGURES II, III, and IV ari:l diagrammatic representations of several prototypic ce s.

FIGURE II shows a gravity flow cell in which the liquid, entering the cell through tube A, is caused to flow by hydrostatic pressure in a continuous stream through the cathode compartment and thence (via conduit C) into the base of the cells anode compartment Where it rises along the anode and finally issues from the cell through the tube at E. Hydrogen liberated at the cathode rises against the downward stream of liquid and escapes from that compartment via a vent in its head, while oxygen liberated at the anode moves concurrently upward with the liquid and escapes from that compartment through another vent.

In FIGURES III and IV are given two versions of forced flow cells, the first designed to operate horizontally and the second vertically. In these cells the solution to be oxidized is pumped into the cathode compartment through a tube located at A. The solution flows through that compartment and, together with the liberated hydrogen, leaves that compartment at B and is carried by conduit C to a surge tank where the hydrogen escapes through a vent. The solution, now freed of hydrogen, is carried by conduit C to a pump which forces the solution into the cells anode compartment at D. Traversing the anode compartment, the solution, together with the entrained, anodically-liberated oxygen, leaves that compartment at E and passes to a second surge tank where the oxygen is vented, and the oxidized solution of the polyvalent metallic ion salt passes on to the use for which it is intended.

It is to be understood that simple cells of the type shown in FIGURES II, III, and IV can, with advantage, be arranged into more complex assemblies, either in a parallel or in a series manner, such that each component cell functions as a modular unit within the whole. In FIG- URE V is shown one such assembly in which a group of five forced flow cells is arranged in parallel as modular units within a pile or stack. A further elaboration of the basic principle is possible by using two or more piles in series, each operating with a particularly advantageous current density and/ or a particular electrode material, and each carrying the oxidation through a different stage of completion (e.g., 20%, 2040%, etc.) such that an optimization of the process overall economics results. moreover, when a series of piles is employed, it is possible to achieve a certain degree of completion in an individual pile by recycling the solution through that piles anode compartments, a slip stream of the solution being passed on to the next stage. In such a series of piles it is to be understood that the flow of solution is always from cathode compartment to cathode compartment, and from anode compartment to anode compartment, except in the last of the series of piles where the flow is from cathode compartment to anode compartment.

It has been found that in practice the functioning of these flow cells continuously is preferable and is improved if there is inserted between the electrodes and the membrane partitions (and, in the case of the gravity flow cell as illustrated in FIGURE II, also between the electrodes and the external cell walls), lattices or grids made of chemically inert and non-conducting materials. For example, it has been found that sections of poly(ethylene) or poly(tetrafiuoroethylene) matting, similar in geometry to the expanded metal mesh used for plaster lath, is useful, and, in forced flow cells, tortuous path spacers,

as for example, the type described in US. 2,891,899 and intended for electrodialysis applications, are particularly well suited to this purpose. Their employ serves to insure good contact of the flowing liquid with the electrode, to maintain that flow in the proper direction through the cells compartments, and to prevent the establishment therein of stationary pockets of gas or liquid.

In any chemical manufacturing process which involves the use and repeated re-use of solutions of salts or polyvalent metallic ions as oxidizing agents, it is highly desirable that the concentrations of the metallic ions and of their accompanying acid anions 'shall be maintained within certain limits. For example, in the case where a solution of thallium(III) sulfate is used to oxidize styrene to phenylacetaldehyde, the concentrations of the thallium and of the sulfate ions should be maintained at such levels that the thallium(I) does not precipitate either as thallium(I) sulfate or as a complex salt with thallium(III) sulfate, nor the thallium(III) precipitate as the insoluble oxide in the event the sulfate ion concentration should become too low. This should be done while maintaniing sufficiently high concentrations of the thallium ion to cause the oxidation to proceed as quickly as possible in equipment of fixed and minimum size. Accordingly, any process which is used to reoxidize the metallic ion to its higher valent state should do so in such a way that harmful or deleterious by-products are not introduced and which yet makes it possible to maintain or to re-establish the desired concentrations of the metallic ion and of its accompanying acid anion both cheaply and efiiciently. This desideratum is successfully accomplished in the present invention by a process employing a membrane-divided electrolytic cell wherein the solution of the polyvalent metallic salt which is to be oxidized flows in a continuous stream, first through the cells cathode compartment, and then through the anode compartment, and by the addition of sufiicient water at a suitable point in the cycle to compensate for the electrolytic loss in the reaction:

wherein M is the polyvalent metallic ion and n is an integer.

The following examples will further illustrate how the invention may be practiced.

EXAMPLE 1 The electrolytic cell used was a gravity flow cell measuring 7" in height, 3" in breadth, and /1" in thickness, similar to the one illustrated in FIGURE II, except that in place of conduit C a pair of small apertures was made in the base of the dividing membrane (anion exchange membrane) to permit the solution to pass from the cathode compartment into the anode compartment. In the cathode compartment of this cell there was inserted a piece of platinized platinum sheeting measuring 6" in length by 1 /2" in width, sandwiched between a pair of plastic grids, each having a thickness of approximately and a length and breadth sufficient to extend from side-to-side and toptobottom of the compartment. In the anode compartment was inserted a similar sandwich, except that in this case the platinum was not platinized. The two electrodes were connected to an electrical source and a ml. portion of an aqueous solution containing 0.344 g. ion (Tl)+ and 1.20 g. ion (SO per liter was placed in the cell. A current of 5.0 amps was applied to the electrodes, and, simultaneously, additional thallium (I) sulfate solution was added dropwise to the cells cathode compartment at the rate of 2.6 ml. per minute, causing the solution to be expelled from an overflow near the top of the cells anode compartment. Electrolysis was continued in this manner for a total of minutes, the efiluent solution being collected separately for the time intervals 050 minutes, 50- 100 minutes, and l00150 minutes. It was found that the efiluents collected during the second and third intervals, which are representative of the process in continuous operation, had 85% and 87% of their thallium content in the trivalent state, corresponding to current efiiciencies of 45% and 46% respectively.

In the following table, the data of the above example (given under the heading of 1c) is summarized with three related exmaples, of which 1a and 1b demonstrate how the conversion and efiiciency of the process are effected by altering the amperage, while example 1d shows the reproducibility of the work.

In general, to obtain the optimum benefits of this invention, the concentrations of the thallium or cerium ions present in the solutions should be as high as possible, but not so high as to incur the precipitation of any solids from the solutions as the electrolysis proceeds. For example, in the case of thallium sulphate, I have found that solutions containing as much as 0.45 gram ion of thallium and 2.0 grams ion of sulphate per liter of solution can be employed at temperatures above about 20 C. and yet not cause the precipitation of either thallium (III) oxides, thallium (I) sulphate, nor any complexes of thallium (I) and thallium (III) sulphates.

TABLE I Example Number 1a 1b 1c 1d 0. 351 0. 344 0. 317 1. 20 1. 20 1. 12 4. 5. 0 5. 0 5. 3 6. 1 6. 2 Thallium Ion Content:

Efifluent (percent): t= 50 min.:

[Tl 50 61 70 69 [T1 46 32 24 27 t= 100 min [T1]+ 69 80 85 84 ['ll]+ 30 19 18 17 t= 150 min [Tl 70 79 87 85 [Tl 3O 21 17 18 Cell (percent):

['Il]+ 53 47 52 51 ll]+ 56 54 52 53 Efiiciency (over-all) (percent) 84 67 52 47 Temperature C.) 30. 33.0 39. 0 38. 5

EXAMPLE 2 The same cell, procedure, and thallium (I) sulfate solution were employed as in Example 10, except that cation exchange membrane was employed. It was found that the efiluents collected during the second and third intervals contained 84% and 86% of their thallium in the trivalent state, corresponding to an average current efficiency of 46%.

EXAMPLE 3 Eessentially the same cell, procedure, and thallium (I) sulfate solution were employed as in Example 2, except that the anode was platinized platinum and that the membrane was a cation exchange membrane. During the period of steady state operation the conversion was 86% and the current efficiency was 63 EXAMPLE 4 Essentially the same cell, procedure, and thallium (I) sulfate solution were employed as in Example 2, except that a microfibreglass mat, for thin layer chromatography, was used as the cell divider in place of the ion exchange membrane. It was found that during the period of steady state operation the conversion to thallium (III) amounted to 73% with a corresponding current efiicency of 52%.

EXAMPLE 5 The cell and procedure were the same as employed in Example 3, however, the membrane was a slightly different cationic exchange membrane and the solution was the nitrate salt of thallium (I) and contained 0.146 g. ion [Tl] and 1.6 g. ion [NO per liter. Additionally, a current of 2.6 amps, rather than 5 amps was used. During the period of steady state operation the conversion amounted to 83% while the current efiiclency was 38%.

EXAMPLE 6 The cell, procedure, and thallium (I) sulfate solution were essentially the same as in Example 2, but the anode was a sheet of lead. During the period of steady state operation the conversion was 75% and the efficienc was 50%.

EXAMPLE 7 The cell, procedure, and thallium (I) sulfate solution were essentially the same as in Example 2, but the membrane was a cellulose ester filter sheet. During the period of steady state operation the conversion was 82% and the efficiency 55% EXAMPLE 8 The cell and procedure were essentially the same as used in Example 2, however the solution was a cerium (III) sulfate solution containing 0.151 g. ion [Ce] per liter and approximately 1.1 g. ion [SO.,]* per liter. A current of 1.0 ampere was employed. Under these conditions it .was found that during the period of steady state operation the conversion to cerium (IV) was 68% with an average efliciency of 40%.

What is claimed is:

1. A continuous process for the electrolytic oxidation of a solution of a salt of a polyvalent metallic ion selected from the group consisting of solutions of thallium (I) and cerium (III) salts which comprises continuously passing the solution to be oxidized into the cathode compartment of a divided electrolytic cell across whose electrodes a difference in electrical potential is imposed, removing the cathodically generated hydrogen and passing said solution into the anode compartment of said cell wherein oxidation (of said polyvalent metallic ion occurs, removing anodically generated oxygen and recovering the resultant oxidized polyvalent metallic ion solution, the cells divider being a membrane which, while it impedes the back-migration of the oxidized metallic ion into the cells cathode compartment, permits transport therethrough of the electrical current-carrying hydrogen ion, the electrode materials being essentially chemically inert and, in the case of the cathode, providing a sufiiciently low hydrogen over-voltage as to prevent the reduction of the metallic ion to its zerofivalent state; and, in the case of the anode, affording a sufficiently high oxygen over-voltage as to effect the oxidation of the metallic ion to its higher valent state in competition with the electrolytic liberation of oxygen from the solvent.

2. The process of claim 1 in which the polyvalent metallic ion is thallium (I).

3. The process of claim 1 in which the polyvalent metallic ion is cerium (III).

4. The process of claim 1 in which an anode is employed of such a character that substantial oxidation of the. metallic ion in competition with the liberation of oxygen is accomplished by the intermediate agency of a strong chemi- 'cal oxidizing agent which is concomitantly generated at the anode-solution interface under the conditions of electrolysis.

References Cited UNITED STATES PATENTS 729,502 5/1903 Moest 20478 1,707,450 4/1929 Sommer 20493 3,147,203 9/1964 Klass 20478 JOHN H. MACK, Primary Examiner H. M. FLOURNOY, Assistant Examiner US. Cl. X.R. 20478 

